TUESDAY, March 26 (HealthDay News) -- Low levels of vitamin D during pregnancy are associated with an increased risk of complications in mothers-to-be and low birth weight in their newborns, a new study finds.

The research shows an association but doesn't prove that insufficient vitamin D causes complications. Still, taking vitamin D supplements may help reduce these risks, the researchers noted.

Researchers examined data from 31 studies published between 1980 and 2012. The studies had between 95 and 1,100 participants.

The analysis revealed that pregnant women with low levels of vitamin D were more likely to develop gestational diabetes (diabetes during pregnancy) and preeclampsia (high blood pressure and protein in the urine). They were also more likely to have a low birth weight baby.

The findings, published online March 26 in the BMJ, are "concerning" given recent evidence that low levels of vitamin D are common during pregnancy, particularly among vegetarians, women with limited sun exposure and those with darker skin, the researchers said.

The body makes vitamin D when the skin is exposed to sunlight. Other sources include supplements and certain types of foods, such as fish. Milk is usually fortified with vitamin D.

While the study identified a significant association between low vitamin D levels and an increased risk for pregnancy complications, further research is need to determine whether programs to boost vitamin D levels in pregnant women would reduce those risks, the researchers at the University of Calgary in Canada wrote.

The findings support a goal of ensuring that all pregnant women have adequate levels of vitamin D, according to an accompanying editorial by Robyn Lucas, of the National Center for Epidemiology and Population Health at the Australian National University in Canberra.

She said that vitamin D "supplements, diet and sunlight exposure" are all measures that "should be used together, with care." Large, well-controlled studies are still needed to clarify the association between too little vitamin D in pregnancy and birth complications, she said in a journal news release.